"This is something you can tell your kids and your grandkids," said Mrs. Obama, who appeared giddy with excitement as she pointed to the celebrated white building looming above rows of carefully arranged blue and white tents. "Do you understand the impact, the importance of this moment today? It's exciting."

As honorary national president of the Girl Scouts, the first lady welcomed the fourth-graders for the evening, which was arranged as part of her Let's Move initiative against childhood obesity. One component of the program encourages kids and their families to take advantage of the outdoors.

The girls, who represent Girl Scout councils in Maryland, West Virginia, Virginia, the District of Columbia and Oklahoma, spent the afternoon climbing a rock wall, tying knots, pitching tents and participating in orienteering exercises to earn a new outdoor badge.

After dark, the girls sang songs and gazed up at the stars under instruction from NASA staff and scientists, including astronaut Cady Coleman, before calling it a night and settling into sleeping bags inside their two-person tents. About 20 chaperones were also spending the night outside.

The White House declined to say whether the first lady would trade her second-floor bedroom for a tent, too.

A trio of Girl Scouts get a Presidential hug during the campout. (Chip Somodevilla/Getty Images)

At one point, the scouts squealed upon realizing that President Obama was approaching their singing circle, accompanied by the first lady.

"What are you guys doing in my yard?" he said, before taking a seat on a hay bale. "When did you guys show up here?"

Obama said his tents weren't as nice and his chairs weren't as cool when he went camping as a boy. He clapped and swayed to music from a guitar player as the girls sang, seated in a circle around lanterns that took the place of what ordinarily would be a roaring campfire.

Members of the Girl Scouts participate in the first-ever White House Campout as night falls. (Alex Wong/Getty Images)

The girls swarmed him when, asked for a hug, he suggested a group hug instead.

"You guys aren't going to be making a racket, are you?" he said, before leaving and returning for a quick look at Saturn through a NASA telescope.

Mrs. Obama, who was not a Girl Scout, said earlier that she didn't know if she could "officially earn a badge but I want to try."

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"I don't know anything. I don't know how to tie a knot. I don't know how to pitch a tent," she said, before drawing a proverbial line against one of their activities. "I'm definitely not climbing that wall."

She did, however, master the art of tying the overhand knot and the square knot.

The campout was co-sponsored by the Interior Department and celebrates the 100th anniversary of the National Park Service.